The present invention relates to a recording medium for thermal transfer recording for use in a thermal transfer recording system printer or the like, for example.
Recently, there are widely used thermal transfer recording system printers which have advantages, such as easy maintenance and small noise.
A recording medium for thermal transfer recording used in this system has a film-shaped backing and an ink layer on the film-shaped backing in which the ink can be recorded on a transferred material, such as paper, plastic film or the like, with application of heat generated from a thermal head.
The ink layer of the recording medium for thermal transfer recording of this kind is made of a thermally fusible material which is mainly made of a wax and so on having small polarity. Therefore, there is then the disadvantage that the above-mentioned ink layer cannot satisfactorily adhere to the film made of a plastic having high polarity, such as polyester, polyimide, or polycarbonate.
Therefore, when such recording medium for thermal transfer recording is loaded into a printer, it is sometimes observed that because the backing is wrinkled or folded, the ink layer is detached from the backing and the ink is trailed from a printed portion during printing (this phenomenon will hereinafter be referred to as a trail of the ink, in which the ink layer is transferred to not only a target transferred portion but also a succeeding portion thereof).
Recently, it is proposed that a primer layer is formed between the backing and the ink layer to increase adhesion therebetween.
However, the proposed recording medium having the primer layer is encountered by the following problems.
Indeed, when a resin primer is used, the adhesion between the backing and the ink layer is improved. But, when printing is carried out at high speed and at high temperature, e.g., at 40.degree. C., it is sometimes observed that a sticking and a jerky printing, both of which will be described later, are caused. The sticking is a phenomenon in which the ink layer is transferred to the transferred object but is not detached from the backing with the result that the transferred object and the recording medium for thermal transfer recording are integrally conveyed and wound around a takeup shaft. The jerky printing is a phenomenon in which when the ink layer is not detached from the backing smoothly, i.e., when the ink layer is detached therefrom intermittently, a recorded object includes a blank line portion formed in the direction perpendicular to the direction in which the recorded object and the recording medium are conveyed.
Surveyance of the inventors of the present invention reveals that the above phenomena are caused by the following cause.
Specifically, printing is carried out by detaching the ink layer from the backing. High printing speed is equivalent to high detachment speed in rheological terminology. As a result of high detachment speed, intensive detaching force between the ink layer and the backing is required for printing at high speed, so that the ink layer is not detached from the backing to thereby cause the sticking and the jerky printing.
At high ambient temperature, resin of the primer layer becomes soft and adsorbs the ink of the ink layer well, so that cohesive failure in the primer layer should be caused to transfer the ink layer. Therefore, intensive detaching force is required for detaching the ink layer from the backing. As described above, with the above recording medium, when printing is carried out at high speed and in a high ambient temperature, smooth printing could not be carried out.